The proposed research is designed to develop well-characterized transcription system which will demonstrate specificity of initiation and termination in vitro. The 35S rRNA and 5S rRNA genes from Tetrahymena pyriformis will be employed as the templates for the purified form I and form IIIRNA polymerases. The base sequences of the 5' and 3' terminal oligonucleotides of the in vivo 35S rRNA and 5S rRNA primary transcripts will be determined and used as an assay for in vitro transcription specificity. The 35S rRNA and 5S rRNA genes will be cloned and their physical maps determined by analysis of the restriction endonucleases digestion products. The sites for transcription initiation and termination will be identified and their DNA sequence determined. Regulation of the transcription of the 35S rRNA and 5S rRNA genes in starved and refed cells will be investigated at both the RNA polymerase and chromatin level. A processing endonuclease which cleaves the 35S rRNA precursor in vitro will be isolated and characterized. The terminal oligonucleotides of the in vivo processing intermediates will be determined and compared to those of the in vitro processing products. The processing endonuclease recognition site will be identified and its nucleotide sequence determined.